Here's what other sites are saying:
Wear the Craft Cool Long-Sleeve T-Shirt under your jersey, and you'll hardly notice the sweat you're working up. Craft utilizes ProCOOL fabric with hollow-filament fibers to wick moisture away from the skin as fast as you can sweat it out. Mesh fabric in critical areas promotes airflow across your body to keep you cool while you're banging out hill repeats.
- Backcountry.com refers to the men's version